What Is a Resettable Fuse?

The resettable fuse is composed of a specially treated polymer resin (Polymer) and conductive particles (Carbon Black) distributed inside. Under normal operation, the polymer resin tightly binds the conductive particles outside the crystalline structure to form a chain-shaped conductive electrical path. At this time, the recoverable fuse is in a low-resistance state (a), which is generated by the current flowing through the recoverable fuse on the line. The thermal energy is small and will not change the crystal structure. When the circuit is short-circuited or overloaded, the heat generated by the large current flowing through the recoverable fuse melts the polymer resin, rapidly growing in volume, forming a high-resistance state (b), and the operating current is rapidly reduced, thereby limiting and protecting the circuit.

Resettable fuse

The resettable fuse is composed of a specially treated polymer resin (Polymer) and conductive particles (Carbon Black) distributed inside. Under normal operation, the polymer resin tightly binds the conductive particles outside the crystalline structure to form a chain-shaped conductive electrical path. At this time, the recoverable fuse is in a low-resistance state (a), which is generated by the current flowing through the recoverable fuse on the line. The thermal energy is small and will not change the crystal structure. When the circuit is short-circuited or overloaded, the heat generated by the large current flowing through the recoverable fuse melts the polymer resin, rapidly growing in volume, forming a high-resistance state (b), and the operating current is rapidly reduced, thereby limiting and protecting the circuit.

By definition, PPTC (Polymer PositiveTemperature Coefficient) is called a resettable fuse. ResettableFuse type fuses are resettable fuses.

Chinese name

Resettable fuse

Constitute

Polymer resin and conductive particles

Function

Effectively protect the circuit

Advantages

No manual replacement required

After the fault is removed, the PTC can restore the fuse to re-cool and crystallize, the volume shrinks, and the conductive particles form a conductive path again. The fuse can be restored to a low resistance state.

60V005 30V090 250V060 16V300 16V090

60V010 30V110 250V080 16V400 16V110

60V017 30V135 250V090 16V500 16V135

60V020 30V160 250V110 16V600 16V160

60V025 30V185 250V120 16V700 16V185

60V030 30V250 250V145 16V800 16V250

60V040 30V300 250V180 16V900

60V050 30V400 250V200 16V1000

60V065 30V500 250V400 16V1100

60V075 30V600 250V600 16V1200

60V090 30V700 250V800 16V1400

60V110 30V800 250V1000

60V135 30V900 250V1200

60V160 250V1400

60V185 250V2000

60V250 600V

60V300

60V375

Note: 60V, 30V, etc. are the maximum withstand voltage units are V; the following numbers 025, 900, etc. refer to the maximum withstand current, the unit is mA.

According to the PCB design space installation requirements, determine the DIP plug-in type or SMD patch type or overcurrent protection chip type; according to the short-circuit voltage V in the circuit, according to the PPTC maximum working voltage Vmax greater than or equal to V, select a certain series of PPTC; Such as 72/30 series; according to the average operating current I in the circuit, the highest ambient temperature T in the circuit, calculate the normal temperature operating current Ih value of the circuit according to the ambient temperature and current reduction ratio, Ih = I / temperature reduction ratio In the selected series, determine that the PPTC operating current is slightly greater than or equal to the Ih value; according to the minimum protection current value and protection time value of the protected circuit, find the closest one on the IT curve of the model selected in 1.2.3 Point, then the curve at this point is the final determination of the PPTC model required by the customer.

Customer quick selection table:

1 . Please fill in the following table according to the parameters of the actual circuit, you can quickly determine the model you need;

Product appearance: DIP plug-in type, SMD chip type, overcurrent protection chip type, AI taping type;

Circuit short circuit maximum voltage (volts), circuit normal operating voltage (volts), circuit maximum operating ambient temperature (degrees), circuit average operating current (amps), minimum current of the protected circuit (amps), minimum protection time under current (second ), Temperature working range (degrees), maximum disconnection time (seconds), maximum external dimensions (mm);

2 . Please select the required model from the table below;

PPTC installation form, working voltage Vmax, working current Ih, application field

PPTC Product Model:

DIP plug-in type (AC / DC6V, 75mA -3.0A)

Low voltage motor / miner's lamp / motherboard IC, USB / 1394link interface

SN6-XXX (AC / DC16V, 2.0A -14.0A)

Motor vehicle anti-theft device / car main wiring harness / high and low frequency power supply / transformer / electric toy / electric massage chair

SN16-XXX (AC / DC30V, 0.7A -9.0A)

Home Theater / Speaker / Frequency Divider / Magnetic Load / Motor / Vacuum Cleaner / High and Low Frequency Power Charger

SN30-XXX (AC / DC72V, 0.050A -3.75A)

LNB Satellite Receiver / DVD / Car CD / LCD Monitor / Switching Power Supply / Tax Controller / POS Speaker

SN72-XXX (AC / DC90V, 0.15A -0.90A)

Electronic ballast / halogen / fluorescent / health lamp / electronic ballast

SN90-XXX (AC / DC250V, 0.050A -1.0A)

ADSL / XDSL voice splitter / switch / distribution frame security unit / POS / tax control machine / prepayment meter / water meter / high voltage motor

SN250-XXX (SMD chip type, AC / DC6-60V, 0.10A -2.60A)

High-density PCB circuit / IE1394 / network card, circuit gateway router / DVD / switch

SMD1812-XXX (AC / DC6-60V, 0.125A -1.50A)

SMD1206-XXX (AC / DC6-60V, 0.05A -1.50A)

SMD1210-XXX (overcurrent protection chip type, DC12-24V, 0.70A -9.0A)

Rechargeable battery Ni-MH / Ni-Cd / Li-ion

PTCXXX-A / B (AI automatic plug-in taping type, AC / DC06-50V, 0.10A -3.75A)

Fully automated AI plug-in machine SN-AI-XXX

Symbol Description

Ih: maximum working current of ptc element under 25 ambient temperature

Vmax: the maximum operating voltage of the ptc element

It: The minimum current for the ptc element to start protection at 25 ambient temperature

Vmaxi: the maximum voltage that the ptc element can withstand in the blocking state

Imax: ptc component can withstand the maximum current

Rmin: initial minimum resistance of the ptc component

Pdmax: power consumption of ptc element in working state

Rmax: initial maximum resistance before ptc component is not working

Polymer-recoverable fuses have no polarity and small capacitance. They are suitable for AC and DC power supplies and are connected in series with the protected electrical equipment. Lithium-ion batteries often cause accidents such as combustion and explosion due to short circuits or overcharges, and polymer resettable fuses can effectively protect them.

Communication equipment: program-controlled switches, user terminal equipment, main wiring security unit, etc.

Automotive electronics: automotive wiring harnesses, automotive anti-theft devices, automotive micromotors, automotive electronics, etc.

Electronics industry: power ballasts, micro-motors, fire alarms, instruments, etc.

Electrical equipment: satellite receivers, security equipment, speakers, industrial automatic control, etc.